Characterization of an ECF56-family sigma factor from Streptomyces venezuelae reveals a highly conserved regulome

Bacteria often possess alternative sigma factors that initiate the transcription of specific genes under environmental stresses, the largest and most diverse group being the extracytoplasmic function (ECF) sigma factors. The regulation of ECF activity is crucial for ensuring the distinct transcription of stress responsive genes only occurs under the appropriate conditions. While most ECFs are comprised of only the core σ and σ regions, a unique form of ECF sigma factor regulation also contains a C-terminal extension bearing homology to the NTF2 superfamily of protein domains. While previous work has shown that this NTF2 domain can affect transcriptional activity in ECF41 and ECF42, its role in the newly classified ECF56 subgroup is unknown. In this work, we show that truncation of the C-terminus of the ECF56 sigma factor SVEN_4562 of upregulates its activity in a hybrid assay. Through transcriptomics in , we found that this truncated ECF56 sigma factor has a highly conserved promoter sequence . Bioinformatic assays illustrated that deep branches of the phylum contained putative ECF56 promoter motifs identical to those found in the ECF56 regulon. We validated these findings through hybrid assays illustrating that truncated ECF56 sigma factors from phylogenetically diverse activate transcription from these promoters. Importantly, our work shows that the genetic infrastructure of the ECF56 family of sigma factors is highly conserved and performs important functions yet to be understood in .